A university alert released after the shooting described the possible shooter as a white male wearing gray sweat pants, a gray hat with a neon green brim, a maroon hoodie and backpack.

The campus is the site of the deadliest shooting rampage in U.S. history, and the tragedy led to widespread security changes on campus and at other institutions nationwide.

The April 2007 massacre at Virginia Tech left 33 people dead, including the gunman, Seung-hui Cho, who turned his weapon on himself before authorities could capture him.

Cho, 23, fired more than 100 shots at his 32 victims, many of whom were crouched in defensive positions at the time they were killed. The university faced widespread criticism and fines in the wake of the shooting. Critics said the university waited two hours after the first bullets were fired -- and two students were killed -- to issue a campuswide alert. Less than half an hour after an alert was finally emailed, 30 others were slain elsewhere on campus by the same gunman.

Cho had been detained previously by campus police investigating allegations that he was stalking female students, and was held at a nearby private mental health facility. He was deemed to be an "imminent danger to self or others as a result of mental illness" but Cho still ended back on campus.